With advances in information processing technologies in recent years, roles played by information processing systems and storage systems are rapidly increasing. Demands on the information processing systems and storage systems for higher performance, higher reliability and larger capacity are growing significantly. In network technologies there is also a growing demand for faster speed.
As one of such super-fast gigabit network technologies a fiber channel (FC) is known. Using the FC allows a plurality of hard disk drives and a controller of the storage system to be connected in loop to build a storage system. Among the connection methods using the fiber channel (FC) loop is a fiber channel-arbitrated loop (FC-AL). The FC-AL connects a controller of the storage system and hard disk drives in a loop.
In the event that the FC loop breaks or fails even at one location, communication between the controller and the hard disk drives is rendered impossible because of the standard specification of the FC loop and therefore the entire FC loop in which a trouble has occurred is removed out of service.
To allow for replacement of hard disk drives and also deal with their failures, a port bypass circuit (PBC) is provided to bypass (disconnect) a part of the FC loop or hard disk drives.
The controller needs to switch the PBC to control the loop so that the entire loop will not be affected by a failed portion of the loop.